In a typical aircraft engine fuel system architecture the fuel supplied to the engine(s) from the airplane's fuel tank(s) by a low pressure pump that is located upstream of a fuel-to-oil heat exchanger. The fuel-to-oil heat exchanger is the main heat sink for the engine oil and provides for both oil cooling and fuel heating.
In such an engine design it is usual to incorporate a bypass flow path providing an alternate flow path for the fuel in the unlikely event that the fuel-to-oil heat exchanger becomes blocked. A typical such engine arrangement is shown schematically in FIG. 1.
Clearly, the engine fuel system must provide the engine with the demanded fuel flow at all operating conditions. The fuel-to-oil heat exchanger bypass arrangement enables this condition to be maintained in the unlikely event that blockage of the fuel-to-oil heat exchanger occurs.
However, even a partial blockage of the fuel-to-oil heat exchanger may result in diminished oil cooling and fuel heating with the performance of both the oil and fuel system deviating from nominal levels for the operating condition of the engine.
It is highly desirable to be able to monitor the on wing health and performance of fuel-to-oil heat exchangers so that the requirement for maintenance action can be forecasted, and/or mitigation action may be taken.